Long standing and difficult problems with alternative fuels such as natural gas and various landfill fuels and mixtures that may be derived from anaerobic processes such as thermal dissociation, endothermic reformation, and/or digestion of sewage, garbage, farm wastes, and forest slash include: chemical and physical property variability, fuel heating value variability, condensates such as water including acid, and other contaminates.
Modern engines and fuel systems are designed to operate with specific fuel characteristics. The variability in the above described, less than optimum sources of fuel have compromised or defeated various past attempts to provide satisfactory power, operational control, drivability, fuel economy, and emissions in instances that alternative fuels have been substituted for gasoline or diesel fuel in internal combustion engines. Even in instances in which elaborate compensations are made to overcome these problems for a specific fuel, when the properties of that fuel vary or if it is desired to switch to another fuel, the fuel system is generally unable to compensate for such large changes in fuel properties.
Accordingly, there is a need for fuel systems and methods for operating internal combustion engines on various, less than optimal fuels while maintaining satisfactory power, operational control, drivability, fuel economy, and emissions standards.